Greg KH, Linux kernel developer delivered a keynote in the Linux plumbing conference about the health of the ecosystem. His message was essentially that distributions that don't contribute to the ecosystem have to rely on the whims of others which is unhealthy for them. Here is an introduction the development model and some interesting statistics about the Linux kernel code. Update by TH: Rebuttals are appearing all over the web, like this one by Canonical's Matt Zimmerman ("He's refuting a claim which has, quite simply, never been made. [...] When this sort of thing happens on mailing lists, it's called trolling."), or this one by another Canonical employee, Dustin Kirkland.

I know of Upstart which seems to be pretty successful and also used in other distributions.

There is also bulletproof-X which is less successful and reportedly can cause problems.

Apart from that I am not really aware of much that Ubuntu has contributed. It may just be that I am ill informed, but my impression is that there is not much else. (and from my erading of some mailing lists, a further problem is that when they DO fix something, they do not always communicate well upstream to let them know a fix is available...)

To me Ubuntu seems to wait for others to do the work, then the marketing spins up and it claims "Great Feature X is now available to Linux users Via Ubuntu!"

(I assume all this can be debunked by a link to a contributions page on the ubuntu website?)